1. Field
This application relates generally to devices and methods for electrical stimulation of biological tissues, and in particular a protocol for flexible communication and control of implanted wireless sensor(s) and microstimulator(s) within the body.
2. Description of Related Art
Electrical signals can be generated within specific tissues by means of miniature implanted capsules, referred to as a “microstimulator”, that receive power and control signals by inductive coupling of magnetic fields generated by an extracorporeal antenna rather than requiring any electrical leads. See, for example, U.S. Pat. Nos. 5,193,539; 5,193,540; 5,324,316; and 5,405,367, each of which is incorporated in its entirety by reference herein. These microstimulators are particularly advantageous because they can be manufactured inexpensively and can be implanted non-surgically by injection. Additionally, each implanted microstimulator can be commanded, at will, to produce a well-localized electrical current pulse of a prescribed magnitude, duration and/or repetition rate sufficient to cause a smoothly graded contraction of the muscle in which the microstimulator is implanted. Further, operation of more than one microstimulator can be coordinated to provide simultaneous or successive stimulation of large numbers of muscles, even over long periods of time.
A microstimulator system is typically composed of a control unit external to the body and several individual microstimulators implanted in the patient which electrically stimulate each muscle. Each microstimulator receives power and data from a transmitter coil worn over the limb and shaped to power all the devices simultaneously. This coil is connected to an external controller that has been programmed to control the movement of the limb. The microstimulators may also performing sensing functions, and such information may be transmitted back to the controller so that the controller can adjust the stimulation parameters.
However, current microstimulator systems present difficulties in controlling stimulation. In particular, it can be difficult to control stimulation of muscles to provide smooth movements and to dynamically increase the strength of muscle contraction. In addition, communication errors between the controller and the microstimulators may cause harm to the patient, such as excessive muscle contraction.